RESEARCH ARTICLE Scanning electron microscopic and histological studies of the buccal cavity of a phytoplanktivorous small freshwater fish, Amblypharyngodon mola Sudarshana Nandi 1,2 | Surjya Kumar Saikia 1 1 Aquatic Ecology and Fish Biology Laboratory, Department of Zoology, Visva-Bharati University, West Bengal, India 2 Department of Zoology, SRM University, Sikkim, India Correspondence Surjya Kumar Saikia, Aquatic Ecology and Fish Biology Laboratory, Department of Zoology, Visva-Bharati University, 731235, West Bengal, India. Email: surjyasurjya@gmail.com Funding information University Grants Commission, Grant/Award Number: UGC-BSR Fellowship Review Editor: Paul Verkade Abstract The electron microscopic and histological studies of the buccal-cavity of herbivorous fish Mola (Amblypharyngodon mola) were performed. The studies revealed that the architectures of the buccal cavity of A. mola support the herbivory nature of the fish. Both the upper and lower jaws of the fish are rich in mucus glands, unculi, and microridges. The presence of papillae like taste buds in the lower jaw of A. mola indi- cates the mechanosensory role of the lower jaw during gustation. These features directly support a gustatory feeding behavior associated with filter feeding in this small freshwater fish. KEYWORDS gustation, mola, mucus gland, small freshwater fish, taste bud 1 | INTRODUCTION Feeding behavior in fish is regulated by several physico-morphological as well as environmental factors. The buccal cavity that starts with the mouth of the fish serves as the main site of entry of food items from the environ- ment into the gut. In fish, lips and other associated organs feature the mouth that helps in searching and processing food during feeding. The buccal cavity in fish often shows diverse modifications facilitating the feeding activity in their environment. Microscopic studies greatly help in understanding such modifications in the buccal cavity in relation to the feeding behavior. This also helps in the characterization of feeding mecha- nisms like suction, filter, ram, and so on. Such characterization not only enforces the production ability of the fish but also in conservation and reduction in management cost of feed under the culture environment. SEM study of the buccal cavity of herbivorous fish, Cirrhinus mrigala, revealed that the fish has gustatory behavior for evaluation and the selection of the preferred palatable food items (Yashpal, Kumari, Mittal, & Mittal, 2009). Similarly, the carnivorous fish Rita rita also not far behind in sensory judgment through taste buds oriented in the buccal cavity (Yashpal, Kumari, Mittal, & Mittal, 2006). It is also reported that omnivorous fishes have more diverse and fine struc- tures around the mouth in comparison to carnivorous and herbivorous fishes to support feeding. For example, Clarias gariepinus possesses several modified structures in their buccal cavity due to their omnivo- rous feeding habit (Gamal, Elsheikh, & Nasr, 2012). Even, different stages of the life of fish, like the juvenile and adult of Dicentrarchus labrax show the architectural differences in their buccal cavities (El- Bakary, 2011). Thus, features in the buccal cavity help in giving a gen- eral idea on the feeding pattern with reference to the feeding habit of the fish (Day, Higham, Holzman, & Wassenbergh, 2015). Amblypharyngodon mola (locally known as “Mola”) is a common freshwater small fish abundantly found in South-East Asia (Figure 1). Along with many other Small freshwater fish species, there are contin- uous efforts to project A. mola as rich animal source of micronutrients (Nandi & Saikia, 2016; Roos, Wahab, Mostafa, & Thilsted, 2007). Nandi and Saikia (2015) worked on the feeding behavior of A. mola and revealed that the fish is herbivorous in nature, and feeds mainly on phytoplankton especially Chlorophyceae (Nandi & Saikia, 2015). Besides Chlorophyceae, the fish also feeds on Cyanophyceae, Bacillariophyceae, and Euglenophyceae (Mamun, Tareq, & Azadi, 2004; Mondal et al., 2013; Nandi & Saikia, 2015; Suresh, Biswas, Vinci, Mitra, & Mukherjee, 2007). With this information on food and feeding of A. mola, it is not known whether it feeds passively through filter feeding or passionately through gustatory or sensory judgment. In vertebrates, since buccal cavity provides direct informa- tion on occurrence of taste buds on tongue, lips, and so on (Gamal Received: 23 May 2020 Revised: 4 July 2020 Accepted: 24 July 2020 DOI: 10.1002/jemt.23572 Microsc Res Tech. 2020;1–6. wileyonlinelibrary.com/journal/jemt © 2020 Wiley Periodicals LLC 1